Electrochemical fatigue sensor (EFS) systems are known in the art as capable of detecting growing cracks due to metal fatigue in metal structures subject to cyclic stress, such as highway bridges. An EFS system for the detection of the fatigue status of a metal structure includes at least two electrochemical sensors, and a potentiostat for applying a polarizing voltage between the structure (substrate) and the sensors, which creates an electrolytic cell. EFS sensors useful for such a method are disclosed in WO 2007/040651.
An EFS system works on electrochemical principles. The structure is polarized to create a protective, passive film on the surface to be tested. A polarizing voltage between the structure and the electrode produces a DC base current in the cell. If the structure being interrogated by the EFS undergoes a cyclic stress, then the current flowing in the cell fluctuates in a complex relation to the variation of the mechanical stress state. Thus, an AC current is superimposed on the DC base current during cyclic stress. Depending on the material of the structure and the loading conditions as well as the state of the fatigue damage in the structure, the transient current of the cell provides information on the status of the fatigue damage.
Because metal structural members subject to cyclic loading and fatigue are often in difficult-to-access locations, remote sensing is an attractive means by which to monitor such locations. Sensing devices for remote use, with sensors and a wireless link to a central computer, are known. See for example the wireless gas monitor marketed by Global Security Solutions.
EFS systems are acquiring increasing importance as a monitoring tool for aging infrastructure, in particular highway bridges. Many bridges currently in use are past their planned life spans, and carrying more traffic than intended, and metal fatigue is a substantial concern. Accordingly, there is a need for improved inspection methods for inspecting bridges and other older infrastructure.